In the 360 degrees of circular pedaling movement, there are two "dead centers", each occurring when the crankshaft is near the 6 o clock and 11-12 o clock positions. In these spots, it is difficult for the human body to produce much crank power since the tangential pedal forcedirection (shown below) is perpendicular to the preferred force direction of the legs. Thus, when one leg is vertically up and the other down, tangential forces cancel and a situation known as "Power Vacuum" occurs for a very short period of time.

Non-circular chain rings aim at reducing the dead centers by changing the shape of the pedaling path and manipulating the gear ratios so that a rider can minimize time spent in these dead spot and approach pedaling power potential.

It makes sense to me but I can't speak for these types of chain rings since I don't have them. It seems to me that they must be custom made to a rider's pedaling technique to provide any objective feel for higher power. Otherwise, any noticed variation is simply an unwarranted placebo effect. Other known issues are linked to nonrhythmic movement of the knee, front shifting and chain suck.

Apart from the mechanical side, there's also a small self-esteem issue for me to be maverick at the local circuit and ride strange looking stuff. I'm not Cipollini, but neither do I have the capacities of Julich. At the moment, I like what I use and prefer the idea of fully developing my upstroke phase to accelerate through the bottom half of the pedaling circle. This should account for any power variations at the dead spots.

What do you think of non-conventional chain rings? If anyone has had a direct experience, it'll be nice if you share with us some numbers related to the improvements or any other disadvantages you may have observed.